Ballasts with integrally insulated base



May 10, 1966 D. LovlNGER BALLASTS WITH INTEGRALLY INSULATED BASE 2 Sheets-Sheet 1 Filed Oct. 23, 1965 May 10, 1966 D. LOVINGER 3,250,956

BALLASTS WITH INTEGRALLY INSULATED BASE Filed Oct. 23, 1963 2 Sheets-Sheet 2 United States Patent O 3,250,956 BALLASTS WITH INTEGRALLY INSULATED BASE Daniel Lovinger, Danville, Ill., assigner to General Electric Company, a corporation of New York Filed O'ct. 23, 1963, Ser. No. 318,402 7 Claims. (Cl. 317-99) This invention relates generally to ballasts for operat` ing electric discharge devices, such as fluorescent lamps. More particularly, it relates to such ballasts having improved thermal and sound characteristics.

Since fluorescent lamps are electric discharge devices and have a negative resistance characteristic, they cannot be usually started by simply connecting the lamps directly across a power supply. Generally, iluorescent lamps require a starting voltage that is higher than the operating voltage. Also, they require a means to limit the lamp current because of the inherent negative resistance characteristic of the lamps.

In fluorescent lamp ballasts the voltage required to start the lamps is usually provided by a shell type of transformer or reactor, which also provides :at least a part of the reactance for limi-ting the current ilow to the lamps. In addition, the ballast may include components such as radio interference suppression capacitors, resistors, liquid impregnated power fact-or correcting capacitors, insulated lead cables, terminal pads and ground insulation strips.

The components are usually housed in an elongated brickshaped case fabricated from sheet metal, and the case is iilled with an asphaltic or resinous type of material. This -lling material provides a path for transfer of heat from the components for dissipation to the ambient environment and also serves to minimize the effect of noise generated by the electrical components of the ballast. It will, of course, be appreciated that the transformers and reactors used in ballasts Aare made up of laminated core structures and copper windings that produce heat and are a source of audible radiation.

The ballast cases generally used at the present time consist of a box having four elongated walls land a pair of end walls. The end walls are usually constructed With ilanges to permit the ballast to be secured to the fixture or -other mounting surface. Further, one of the elongated'walls serves as av coverplate and is usually'not attached to the ballast case until the final steps of assembly have been completed. In many ballasts the coverplate also serves as the base or the wall of the ballast case that adjoins the xture or other mounting surface.

Circuit connections between the leads, which extend out of the ballast case for connecting the ballast in circuit with the power supply and the lamps, and the various ballast components are conventionally made on one side of the core and coil assembly. In order to prevent the terminal connections and bare leads from possible grounding by contacting one of the walls of the ballast case, a strip of insulating material made of treated paper is usually placed between the side of the core andA coil assembly on which the connections are made and the adjacent wall of the ballast case.

Heretofore, one of the difculties encountered as a result of the use of paper strip as ground insulation in fluorescent lamp ballasts is that the strip frequently impairs the heat conduction to the base of the ballast case. Changing the location of the terminal connections so that the ground insulation strip is placed between the core an-d coil assembly and the top wall of the ballast case or the wall opposite to the base, has not provided an entirely satisfactory solution to the problem. For example, in the ballast arrangement shown -in FIGURE l of U.S. Patent 2,869,037 Brooks et al., the connections to lthe various leads are disposed between the top side of the core and ICC coil assembly and the top wall of the ballast case so that base-side of the core and coil assembly can butt directly against the base of the ballast case thereby to provide for a more effective transfer of heat by conduction to the base and the lamp xture. Although in such a ballast arrangement the heat transfer between the ballast components Y `and Vthe b-ase of the ballast case is improved, the insulating strip between the components and the top wall of the ballast case has presented problems, which 4are usually encountered in applications where paper strips are used for ground insulation.

A problem frequently encountered with paper ground insulation strips is that the strip is not always securely positioned against the wall of the ballast case. The lack of contact between the strip and the :adjacent wall, in ellect, allows the Wall to act as a sounding board for the loose strip whenever the strip rattles during operation to thereby increase the noise level of the ballast. Another problem encountered with paper ground insulation strips is that the strips tend to move, when hot `asphaltic compound or other lling material is poured in the case during the potting operation, and the'terminal connections are exposed to possible grounding. Further, the penetration or puncture resistance of commonly used ground insulation 'strip materials has not been satisfactory in practice. As -a result, failures of ballasts may occur when a soldered terminal connection penetrates through the paper strip and becomes grounded to the metallic case.

In view of the foregoing considerations, it will be appreciated that there has been a long standing need in the ballast industry for an improved arrangement for insulating the exposed leads and terminal connections in a ballas-t from the case.

Accordingly, a general object of the present invention is to provide an improved ground insulation arrangement for the terminal connections and leads in a ballast for operating electric discharge devices such as lluorescent lamps.

It is a more specific object of the present invention to provide a ground insulation arrangement in a ball-ast that does not impede the transfer of heat by conduction from the internal components of theballast to the walls of the ballast case for dissipation to the ambient environment.

Another object of the present invention is to provide an improved ground insulation arrangement in a ballast wherein the ground insulation-means does not impair the sound characteristics of the ballast.

It is still a further object of the invention to provide an improved ground insulation arrangement for a ballast that is readily -adaptable to automated or semiautomated type of assembly techniques.

Another more specic object of the invention is to provide Ia ground insulation means having improved puncture res1stance.

In accordance with one form of my invention I have provided an improved ground insulation arrangement for a fluorescent lamp ballast wherein at least one ofthe elongated walls of the ballast case is provided with integral resin iilm coating, preferably a thermosetting epoxy resin. The -lm insulation is integrally formed on the inner surface of the wall adjacent to the side of the coils on which leads and terminal connections are disposed. The interior of the case is lled with compound which intimately contacts the integral resin film for establishing a thermally conductive path therebetween.

The integrally insulated wall arrangement of the ballast case not only prevents the components of the ballast from grounding to the case |but also results in improving the thermal and the sound characteristics of the ballast. Further, the integrally insulated wall arrangement results in improved puncture resistance as compared with conven` tional treated paper strip insulation -and is readily adaptable to automated a-nd semiautomated production techniques.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the con- -cluding portion of the specification. My invention, however, both as to organization and method of operation, together with further objects and advantages thereof may best -be understood by reference to the following description taken in conjunction with the accompanying drawing in which:

.FIGURE 1 is a side view of a ball-ast with the case and filling compound cut-away to show the improved insulating wall arrangement;

FIGURE 2 is a sectional view of the ballast illustrated -in FIGURE 1 taken generally along line 2 2 and showing the entire cross-section of the ballast;

FIGURE `3 is a side view of another ballast embodying the invention, the side of the case and the filling compound being cut away to show the internal arrangement;

FIGURE 4 is a sectional view of the ballast illustrated in FIGURE 3 taken generally along line 4-4 and showing the entire cross-section of the entire ballast;

FIGURE 5 is a simplified diagrammatic illustration in perspective of the apparatus used to apply the integral insulation to the coverplate of the ballast case, the apparatus and coverpl-ate being partially cutaway;

FIGURE 6 is a sectional view of the apparatus shown in FIGURES taken along line 6 6;

FIGURE 7 is a view in perspective of the lcoverplate with the inner surface coated with a thin integral resin film of insulation, the coverplate and film being partially cutaway; l

FIGURE 8 `is a view in perspective of another apparatus used to apply the integral insulation, the apparatus and applicator being partially cutaway; and

FIGURE 9 is a sectional view of the applicator shown in FIGURE 8.

Referring now to FIGURES 1 and 2 of the drawings, there is illustrated therein an improved ballast 10 for starting and operating fiuorescent lamps (not shown). The ballast 10 is provided with flanges 11 and 12 so that the ballast 10 can be secured by screws or other suitable fastening means in the channel of a fluorescent lamp fixture or other suitable mounting surface. The coverplate 13 is brought into firm engagement with the mounting surface along the entire length of the coverplate 13 so that heat generated by the components of the ballast 10 and conducted to the coverplate 13 can be transferred by conduction to the mounting surface.

The principal parts of the -ballast 10, as seen in FIG- URES 1 and 2, are a case 14, high reactance transformer 15, a capacitor 16, and the leads 17 which connect the components in operative circuit relation and are brought out of the case 14 for connection to a power supply and to the fluorescent lamp or lamps operated by the ballast 10. The high reactance transformer 15 includes a shell type of magnetic core 18 having electrical coils 19, 20 mounted thereon. As will be seen in the sectional view shown in FIGURE 2, the coil 20 is disposed on a center winding leg 21 between the outer yoke members 22 and 23 of the magnetic core 18. The magnetic core 18 is formed of `a plurality of stacked laminations of magnetic material, such as, for example, silicon steel, which are held in assembled relation by core clamps 24. 'The capacitor 16 is a liquid impregnated paper and aluminum foil capacitor. In addition to other functions, the capacitor 16 serves to correct the power factor.

It will be appreciated that the ballast 10 may include other components, such as -a radio interference suppression capacitor, a starting capacitor, isolating resistors,

etc. Since the present invention is not limited to any specific ballast circuit arrangement, I have not described herelin any particular ballast circuit. For a description of a representative ballast circuit arrangement as may be used in conjunction with the improved arrangement of the present invention, reference may be had to the aforementioned Brooks et al. Patent 2,869,037, which describes a commonly used ballast circuit for operating liuorescent lamps.

In the embodiment of the invention illustrated in FIG- URES 1 and 2, the magnetic core 18 and the coils 19, 20 are disposed in the ballast case 14 so that the terminal connections 25 are made on the side of coils 19, 20 adjacent to the coverplate 13. As will be seen by referring to both FIGURES 1 and 2, the case 14 used to house the components of the ballast 10 is essentially comprised of four elongated walls, one of which is the coverplate 13, and a pair of end Walls 27 and 28. The coverplate or base wall 13 is a separate channel-shaped member that is secured by suitable eyelets 9 or other means to flanged portions 11, 12 of the end walls 27, 28.

In accordance with the invention an integral film 3) of electrically insulating and thermally conducting resin material is applied to the inner surface of the coverplate 13. As used herein, an integral -film is a continuous and adherent coating bonded to a surface, as for example, by applying la thermosetting resin to the surface by film drawing or other method of application and curing the resin in situ.

In the illustrated embodiment of the invention the integral film was `approximately 0.010 of an inch in thickness and provided an effective bonding `surface for the filling compound which was a mixture of asphaltic compounds and silica. Preferably, the material used to form the integral film used on ythe wall or on the ballast case was an epoxy resin, such as the bisphenol-epichlorohydrin polymers. Suitable curing agents for the epoxy resins which may be 'used in the practice of the invention are, for example, the tertiary amines such as the amino phenols. In the illustrated exemplification of the invention the =cur ing time for the epoxy resin used was approximately 30 minutes at a temperature between 145 and 150 degrees centigrade.

In the arrangement shown in FIGURES l and 2, the integral film 30 applied to the coverplate 13 serves to facilitate the conduction of heat between the filling compound 8 to the coverplate or base wall 13 where it is dissipated to a fixture or other surface on which the ballast case 14 is attached. An important advantage of the improved integral film arrangement is that the filling compound 8 effectively adheres or bonds to the integral film 3) on the coverplate 13. This bonding minimizes the possibility `of voids being formed between ythe surface of `the filling compound. Such voids interfere with the heat transfer and may increase the audible sound radiations of the ballast 1li.

In FIGURES 3 and 4 I have shown a ballast 40 in which the plurality of leads 41 brought out from the sides of coils 42 and 43, which are adjacent to the wall 44 of the case 45. The circuit connections 46, 47 with leads 41 are made on terminal pads 48 and 49 supported on clamps Sti and 51. Such a terminal lead arrangement is more fully described and claimed in the copending application Serial Number 243,839 tiled in the name of George W. Beckes et al. on December ll, 1962 and :assigned to the same assignee =as the present invention.

It will be noted that in the embodiment of the invention illustrated in FIGURES 3 and 4, an integral film 53 is formed on the opposite wall 44 of the ballast caseV 45 and not on the coverplate 54 since the exposed lead and terminals are adjacent to the wall 44. The components of the ballast 40, as shown in FIGURES 3 and 4, include a transformer 55, a capacitor 56, and `the case having flanged elements 57 and 58. The magnetic core 59 includes =a center winding leg 6d and outer yoke members 61 and 62.

In the embodiments of the invention illustrated in FIG- URES 1-4 the integral resin film was applied by a nozzle type -of applicator 65 shown in FIGURES 5 and 6. The inlet 66 was connected `to la pressurized liquid resin feeding system (not shown). The liquid resin was fed through an elongated narrow orifice 67 as the coverplate 13 was moved along a channel-shaped guide member 69 supported on a plate 39. After the liquid resin was applied to the coverplate 13 to form a film-drawn coating onthe inner surface, the coverplate 13 was then placed in an oven to accelerate the cure of the resin. The coverplate 13 with the cured integral film 30 formed on the inner surface is illustrated inl FIGURE 7.

Another arrangement for applying the resin to the coverplate 13 is shown in FIGURES 8 and 9. As illustrated therein, the channel-shaped sides of the coverplate 13 are used to guide an applicator 70 as it is moved along the coverplate 13 to spread the liquid resin 69 over the inner surf-ace of the coverplate 13. The applicator 70 includesv an inlet 71 for connection to a supply of resin and an orifice 72 for controlling the supply of liquid resin 69.

In order to demonstrate the important advantages `achieved by the practice of the present invention, temperature readings were taken on a ballast of the type shown in FIGURE 3 and incorporating the improved integrally insulated wall arrangement. Similar temperature readings were taken on identical -ballasts without the improved insulation arrangement, one pair of `ballasts having a conventional insulating strip of treated paper preassembled or attached to the base and another pair of ballasts with ythe insulating strip disposed along the base Without attachment to the base.

In order to take the temperature reading thermocouples were placed on primary coil 43 and on the Wall 44 over the primary coil 43 to determine the temperature at these points while the ballasts operated fiuorescent lamps. During the test runs the ballasts were installed in a fourlamp enclosed fixture. The test results are-summarized in Table I below:

T able I Primary Coil Average Case .From Table I it will be seen that with the improved integral film arrangement, it was possible Vto achieve a rel duction of 2 degrees centigrade in the average case temperature. The lower case temperature indicates that the heat generated within the ballast components is being effectively dissipated thereby insuring a greater life expectancy for the ballast.

In addition to the improved thermal characteristics of the ballast, it is possible with the integral film larrangement of the invent-ion to provide inulation with superior impact or puncture resistance as compared with conventional arrangements. In ballasts utilizing treated paper strips as ground insulation, it is normally expected that about one in two hundred tballasts coming off an assembly line will be rejected because of the penetration of a solder connection or bare wire -lead through the `base insulation strip. However, in `ballasts employing the improved integrally film arrangements failures due to this cause have virtually been eliminated because of the superior puncture resistance of the integral film.

Although I have described herein embodiments of my invention by way of illustration, it will be apparent to those skilled in the art that various changes and modifications may be made `therein without departing from the invention. Although in the illustrative embodiments of the invention the film drawn integral film was applied only to one wall of the ballast case, it will be apparent to those skilled in the art that the integral film may be advantageously applied to other walls of the case. It

is, therefore, intended in the appended claims to cover tioned in said ballast case, the improvement comprising: l

an integral film of electrically insulating and thermally conducting resin material formed on the inner surface of at least one of said Walls, said integral film being disposed between said inner surface and the side of said electrical coils on which leads are exposed thereby to prevent the leads from grounding against the ballast case, and a filling compound disposed within said ballast case to fill the space between the inner surfaces of the ballast case andthe components, said filling compound contacting and bonding to said integral film for establishing a thermally conductive path between said filling compound and said one wall of said ballast case.

2. In the ballast set forth in claim 1 wherein said integral film is comprised of a thermosetting epoxy resin cured to form a solid, infusible film.

3. In a ballast for starting and operating at least one electric discharge device, Isaid ballast being comprised of plurality of components housed in a metallic ballast case having a substantially rectangular cross-section and including four elongated walls and a pair of end walls, said components including a magnetic core, electrical coils disposed thereon, a capacitor, and leads connecting the components in operative circuit relation, the improvement comprising: an integral film of electrically insulating and thermally conducting resin on the inner surface of one of said elongated walls adjacent to the side of the coils on which electrical connections are made, said film providing a puncture resistant surface to prevent said leads from grounding by contacting the wall of said metallic ballast case, and a thermally conducting material bonded to said integral film and filling the interior spaces of the ballast case thereby to substantially encase said components.

4. In the ballast set forth in claim 3 wherein said integral film is comprised of a thermosetting epoxy resin cured to form a solid, infusible and adherent film.

5. In a ballast for operating electric discharge devices, said ballast having a ballast case formed with four walls and a pair of end walls holding a plurality of components including at least a capacitor, a laminated magnetic core with electrical coils disposed thereon, and electrical leads joined at terminals for connecting the coils and capacitor in operative circuit relation, the improvement comprising: a film drawn coating of electrically insulating and thermally conducting resin material on an inner surface of at least one of said Walls, said film drawn coating being disposed between said one Wall and sideof said electrical coils having exposed leads and terminals thereby to prevent the leads and terminals from grounding against the ballast case, and a filling compound disposed within said ballast case to fill the space between the inner surfaces of the ballast case and the components, said filling com pound contacting said film drawn coating for establishing a bonded, heat conduction path between said filling compound and said one Wall.

6. In the ballast set forth in claim 5 wherein said film drawn coating is comprised of a thermosetting epoxy resin cured to form a solid infusible and adherent film.

7. In a ballast for starting and operating at least one fluorescent lamp, said .ballast having a metallic case having four elongated walls, one of said elongated walls being a coverplate, a plurality of components positioned in said case and including a magnetic core, electrical coils dis- 8 posed thereon, a capacitor, and leads connecting the Com- 2,882,505 4/ 1959 Feder 174-52 X ponents of the ballast in operative circuit relation, the 2,889,423 6/ 1959 Yochum 264-272X improvement comprising: an integral lrn of electrically 3,049,579 8/ 1962 Sulzerr '.a 336-96 X insulating and thermally conducting resin on the inner 3,141,049 7/ 1964 Parsons 264-272 X surface of the coverplate, said integral lm providing a 5 Y FOREIGN PATENTS puncture resistant surface to prevent sa1d leads from grounding by contacting said coverplate, and a thermally y 242,040 12/1962 Austfahaconducting potting material containing asphaltic constit- 960,040 6/1964 Great Britain# uents and lling the interior spaces of the ballast case thereby to substantially enease lthe components thereof, 10 OTHERBEFERNCES said potting material contacting and bonding to said in- The Condened Chemical DlClOUafY, Relnhold Publtegral lm to establish a heat conduction path between C0 New Yfk, 1961, QD 5`C5C 12, EPIX 445- said potting material and said coverplate.

LARAMIE E. ASKIN, Primary Examiner. References Cited by the Examiner 15 y l UNITED STATES PATENTS JOHN F. BURNS, ROBERT K. SCHAEFER, Exammm.

1,702,159 2/1929 Grunow 336-96 l F- RUGGIERO, W- B- FREDERICK, 2,194,703 3/ 1940 Kater 174-5051 X .Assistant Examiners. 

1. IN A BALLAST FOR STARTING AND OPERATING ELECTRIC DISCHARGE LAMPS, SAID BALLAST HAVING AN ELONGATED BALLAST CASE FORMED WITH FOUR WALLS AND A PAIR OF END WALLS, AND HAVING COMPONENTS INCLUDING AT LEAST A CAPACITOR, A LAMINATED MAGNETIC CORE WITH ELECTRICAL COILS DISPOSED THEREON, AND ELECTRICAL LEADS CONNECTING THE COILS AND THE CAPACITOR IN OPERATIVE CIRCUIT RELATION, SAID COMPONENTS BEING POSITIONED IN SAID BALLAST CASE, THE IMPROVEMENT COMPRISING: AN INTEGRAL FILM OF ELECTRICALLY INSULATING AND THERMALLY CONDUCTING RESIN MATERIAL FORMED ON THE INNER SURFACE OF AT LEAST OF SAID WALLS, SAID INTEGRAL FILM BEING DISPOSED BETWEEN SAID INNER SURFACE ND THE SIDE OF SAID 